What Is Parallax?

[Sir Henry]

Yes I know what parallax is and can give you a textbook definition. But how much does it really affect accuracy? I have rimfire scopes preset at 60 yards and am wondering if my eye is offset slightly how much will I see off at 50 and 100 yards? How about a centerfire scope set for 150 yards. What if I’m shooting at 50 and 100 yards?

What does SF mean on a scope? Does it have anything to do with parallax?

[Cofisher]

Thanks for asking the question. I need to know more about this subject. I’m betting NCG has the definitive answer.

[GunnyGene]

SF means Side Focus. Basically it's the same as Adjustable Objective, and does the same thing. That is it allows you to adjust the scope to compensate for parallax at different distances. A SF scope will have 3 turrets, the one on the left is your parallax adjustment turret. Set it for the approx. range (or exact range if you know it) to your target. Magnification has an effect on parallax. Higher magnification will result in more of a parallax issue than lower magnification. More detail regarding setting order of power, focus, and parallax adjustment here:

https://www.leupold.com/riflescope-troubleshooting

[JEBar]

here is a link ====> https://www.youtube.com/watch?v=bEKt-bapfK4 to a short video that helped me understand what it is and how to fix it

[Sir Henry]

I think I understand the effect of parallax I want to know how much it really matters. If the scope is set for 60 yards and I’m shooting at 100 yards how far off the aim point will I shoot? Is it 3/8ths of an inch or three inches? Or even 8 inches?

On some scopes the eye box is so small it’s almost impossible to be that fat off center and not know it.

[GunnyGene]

I think I understand the effect of parallax I want to know how much it really matters. If the scope is set for 60 yards and I’m shooting at 100 yards how far off the aim point will I shoot? Is it 3/8ths of an inch or three inches? Or even 8 inches?

On some scopes the eye box is so small it’s almost impossible to be that fat off center and not know it.

Short answer is not much (assuming you have a fixed objective at 100yds, and don't crank in a lot of magnification). Just make sure you have a crisp reticle as noted in the link I posted. At 60 yds (or 140yds) the target will likely be slightly out of focus. Don't adjust your focus to bring the target into clearer focus. Keep your eye focused on the reticle. All parallax adjustment does is bring the target image into the same focal plane as the reticle, giving you crisp target and reticle images. I've never noticed any "floating" effect that video talked about.

Same as focusing on the front sight if you're using irons.

[Sir Henry]

I sure learned a lot today by doing a parallax check on some of my scopes. First of all I would like to say I checked at 75 yards and the distance was determined by this rangefinder.

FAB6C3EA-44B3-4A68-8BF2-D720507B3050.jpeg

I knew SF meant side focus (from reading) and have one.

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What confused me was I thought I had ordered the 4.5-14x50 SF 30mm. Now I remember they were out of stock and I ordered the 4.5-14x 50 1”. So when I received it without the third knob I thought it might mean something else. I think I’m getting senile.

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This is the scope that was on the CZ American I took to Texas and had problems. The picture below is where I experienced no movement for 75 yards. I’ve never had trouble with it befor but it seems it did not survive the 2,000+ mile trip.

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It took me about an hour to setup a stable platform and be able to sight out an open window. I was limited to open windows because I did not want to be aiming rifles in view of neighbors.

What really surprised me was the amount of parallax even between short differences. Easily two inches just between 60 and 75 yards. Aiming a rimfire scope with a fixed parallax of 60 yards would float the crosshairs a foot at 200 yards.

[JEBar]

I've never noticed any "floating" effect that video talked about.

I have noticed the crosshairs floating around but I've always assumed it was my natural wobble ..

[RanchRoper]

I thought parallax was something for constipation.

[Sir Henry]

I've never noticed any "floating" effect that video talked about.

I have noticed the crosshairs floating around but I've always assumed it was my natural wobble ..

I tend to make sure my eye is centered in the eye box and then check the crosshairs. What I’m learning is I need to be cross checking them and give the crosshairs priority in regards to no movement against the intended aim point.

Like I said earlier I could give you a textbook definition without understanding what it really meant. I was shocked at how much movement occurs between small differences from true parallax corrected distances.